Generally, a photolithography process used to manufacture a semiconductor device includes forming a photoresist pattern on a semiconductor substrate. The photolithography process may include a coating step, a baking step, an exposure step, and a development step. The coating step is used to form a photoresist film on the semiconductor substrate, and the baking step is used to harden the photoresist film. The exposure step and the development step are used to transform the photoresist film into a photoresist pattern using a reticle.
The photoresist film on the semiconductor substrate is selectively exposed to light during the exposure process. More particularly, an image of a pattern on a mask is projected on the photoresist film using light from a light source to form the photoresist pattern. If the pattern on the mask is not uniform or the photoresist pattern on the semiconductor substrate is not sufficiently uniform, however, a reliability of the semiconductor device may be reduced. Accordingly, a uniformity of the photoresist patterns may need to be measured using critical dimensions.
Devices used to measure critical dimensions include scatterometers and/or scanning electron microscopes (SEM). A scatterometer uses a diffraction phenomenon generated when projected light is reflected on a material. A scatterometer may measure a critical dimension of a pattern having a bar shape. An SEM may measure critical dimensions of patterns having various shapes because an SEM uses real images of the patterns. Measuring critical dimensions from a mask and/or an entire semiconductor substrate, however, may take a relatively long time.
To measure critical dimensions of photoresist patterns, optic modeling may be used together with a spectrophotometer. If reflectivity or transmittance of photoresist patterns measured by the spectrophotometer is substantially identical to reflectivity or transmittance calculated from simulations, a simulated critical dimension of the photoresist pattern may be set as a critical dimension of the pattern of the mask or the photoresist pattern on the semiconductor substrate. Performing optic modeling, however, may take a long time because the simulations may need to be performed repeatedly.